Prior art is configured using concentric intake and exhaust where both intake and exhaust commute to atmosphere outside a building structure. Concentric passageways are constructed to be coaxial, one pipe within another. Various outside configurations, external to the building structure, are used to shield intake and exhaust gases in order to nullify the effects of outside (atmospheric) air, also known as weather conditions. Intake air is fresh air from outside a building structure. Exhaust is a combination of gases that are the product of a gas fuel burning or the oxidation reduction reaction that occurs when gas fuel is combined with oxygen found in air.
Prior art describes direct vent as communicating with the atmosphere outside a building. Direct vent systems combine the intake and the exhaust pipes into one concentric pipe. Prior art oversizes both exhaust and air intake pipes used for direct venting. In some prior art, exhaust gas moves into a single fitting where intake and exhaust may mingle, and where it dilutes the exhaust gases with intake air before exhausting to the atmosphere.
Prior art uses concentric piping arrangements for the convenience of making one penetration in the building structure. Concentric intake and exhaust is an interior coaxial passageway and a coaxial outer passageway. Both intake and exhaust share a single penetration that allows intake and exhaust to commute to the atmosphere outside a building structure.
Direct vent systems use various types of termination to communicate to the atmosphere outside a building. Termination is that part of the direct vent system that extends outside a building structure and is known as the point of entry for intake air and the point of exit for exhaust air. In termination systems of this type, illustrated in Valters U.S. Pat. No. 5,562,088 the combustion chamber within which the exhaust gases are generated, vents directly through an outside wall to the atmosphere outside of the building structure. Exhaust gases are piped through the center of an intake pipe, coaxially, where the intake commutes atmospheric air to support the combustion (burning) of a gas flame. In this prior art example the termination is attached to the outside of a building where the intake commutes atmospheric air to the gas flame and the exhaust commutes to the atmosphere through the concentric pipe that runs through the center of the intake pipe, coaxially. The termination holds both intake and exhaust pipes in a housing.